Programmable resistive memory cell with oxide layer

ABSTRACT

Programmable metallization memory cells include an electrochemically active electrode and an inert electrode and an ion conductor solid electrolyte material between the electrochemically active electrode and the inert electrode. An electrically insulating oxide layer separates the ion conductor solid electrolyte material from the electrochemically active electrode.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No.61/109,198 filed Oct. 29, 2008, the contents of which is herebyincorporated by reference in its entirety.

BACKGROUND

Memory devices are common in electronic systems and computers to storedata. These memory devices may be volatile memory, where the stored datais lost if the power source is disconnected or removed, or non-volatile,where the stored data is retained even during power interruption. Anexample of a non-volatile memory device is a programmable metallizationcell (PMC).

A PMC utilizes a fast ion conductor such as a chalcogenide-type or anoxide-type (e.g., NiO) and at least two electrodes (e.g., an anode and acathode) with the fast ion conductor between the electrodes. When avoltage is applied across the electrodes, superionic clusters orconducting filaments rapidly grow from the cathode through the fast ionconductor towards the anode. When the clusters or filaments are present,the cell is in a low resistance state. When an electric field ofopposite polarity is applied across the electrodes, the conductingfilaments dissolve and the conducing paths are disrupted, providing thecell with a high resistance state. The two resistance states areswitchable by the application of the appropriate electric field and areused to store the memory data bit of “1” or “0”.

While a high ionic conductive solid electrolyte (e.g., chalcogenide)provides a high speed switch between the two resistance states of thePMC, this material can suffer from poor data state retention. Anotherlower ionic conductive solid electrolyte (e.g., oxide electrolyte)provides for good data state retention, but this material can sufferfrom slow switching between the two resistance states of the PMC. Thus,there is a tradeoff between switching speed and data retention in a PMCcell depending on what solid electrolyte (in regards to the materialproperty differences) is provided in the PMC cell. There is a need for aPMC cell that can provide both fast switching speeds and extended dataretention.

BRIEF SUMMARY

The present disclosure relates to programmable metallization memorycells having an oxide layer separating the solid electrolyte from theelectrochemically active electrode of the programmable metallizationmemory cell.

In one illustrative embodiment, a programmable metallization memory cellincludes an electrochemically active electrode and an inert electrodeand an ion conductor solid electrolyte material between theelectrochemically active electrode and the inert electrode. Anelectrically insulating oxide layer separates the ion conductor solidelectrolyte material from the electrochemically active electrode.

One illustrative method of forming a programmable metallization memorycell includes depositing an ion conductor solid electrolyte layer on aninert electrode, depositing an oxide forming layer on the ion conductorsolid electrolyte layer, and depositing an electrochemically activeelectrode on the oxide forming layer.

These and various other features and advantages will be apparent from areading of the following detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

The disclosure may be more completely understood in consideration of thefollowing detailed description of various embodiments of the disclosurein connection with the accompanying drawings, in which:

FIG. 1A is a schematic side view diagram of an illustrative programmablemetallization memory cell in a low resistance state;

FIG. 1B is schematic side view diagram of the illustrative programmablemetallization memory cell in a high resistance state;

FIG. 2 is a schematic diagram of an illustrative programmablemetallization memory unit including a semiconductor transistor;

FIG. 3 is a schematic diagram of an illustrative programmablemetallization memory array;

FIG. 4 is a flow diagram of an illustrative method of forming aprogrammable metallization memory cell with an oxide layer;

FIGS. 5A-5C are schematic cross-section views of a programmablemetallization memory cell with oxide layer at various stages ofmanufacture;

FIG. 6 is a flow diagram of another illustrative method of forming aprogrammable metallization memory cell with an oxide layer; and

FIGS. 7A-7D are schematic cross-section views of another programmablemetallization memory cell with oxide layer at various stages ofmanufacture.

The figures are not necessarily to scale. Like numbers used in thefigures refer to like components. However, it will be understood thatthe use of a number to refer to a component in a given figure is notintended to limit the component in another figure labeled with the samenumber.

DETAILED DESCRIPTION

In the following description, reference is made to the accompanying setof drawings that form a part hereof and in which are shown by way ofillustration several specific embodiments. It is to be understood thatother embodiments are contemplated and may be made without departingfrom the scope or spirit of the present disclosure. The followingdetailed description, therefore, is not to be taken in a limiting sense.

Unless otherwise indicated, all numbers expressing feature sizes,amounts, and physical properties used in the specification and claimsare to be understood as being modified in all instances by the term“about.” Accordingly, unless indicated to the contrary, the numericalparameters set forth in the foregoing specification and attached claimsare approximations that can vary depending upon the desired propertiessought to be obtained by those skilled in the art utilizing theteachings disclosed herein.

As used in this specification and the appended claims, the singularforms “a”, “an”, and “the” encompass embodiments having pluralreferents, unless the content clearly dictates otherwise. As used inthis specification and the appended claims, the term “or” is generallyemployed in its sense including “and/or” unless the content clearlydictates otherwise.

Spatially related terms, including but not limited to, “lower”, “upper”,“beneath”, “below”, “above”, and “on top”, if used herein, are utilizedfor ease of description to describe spatial relationships of anelement(s) to another. Such spatially related terms encompass differentorientations of the device in use or operation in addition to theparticular orientations depicted in the figures and described herein.For example, if a cell depicted in the figures is turned over or flippedover, portions previously described as below or beneath other elementswould then be above those other elements.

As used herein, when an element, component or layer for example isdescribed as being “on” “connected to”, “coupled with” or “in contactwith” another element, component or layer, it can be directly on,directly connected to, directly coupled with, in direct contact with, orintervening elements, components or layers may be on, connected, coupledor in contact with the particular element, component or layer, forexample. When an element, component or layer for example is referred toas begin “directly on”, “directly connected to”, “directly coupledwith”, or “directly in contact with” another element, there are nointervening elements, components or layers for example.

The present disclosure relates to programmable metallization memorycells having an oxide layer separating the solid electrolyte from theelectrochemically active electrode of the programmable metallizationmemory cell. The oxide layer serves as an ionic barrier layer thathinders or prevents ionic transport between the solid electrolyte andthe electrochemically active electrode of the programmable metallizationmemory cell when an electrical bias is removed from the programmablemetallization memory cell. The oxide layer can be grown when anelectrical bias is removed from the programmable metallization memorycell, and the oxide layer can be converted to a more ionic conductivephase when a negative electrical bias is applied to the programmablemetallization memory cell. Overall, the oxide layer serves as a barrierto ionic transport between the solid electrolyte and theelectrochemically active electrode of the programmable metallizationmemory cell, which enhances cell data state retention. While the presentdisclosure is not so limited, an appreciation of various aspects of thedisclosure will be gained through a discussion of the examples providedbelow.

FIGS. 1A and 1B are cross-sectional schematic diagrams of anillustrative programmable metallization memory cell 10. In FIG. 1A,memory cell 10 is in the low resistance state. In FIG. 1B, cell 10 is inthe high resistance state. Programmable metallization cell (PMC) memoryis based on the physical re-location of superionic regions and formingconducting filaments within an ion conductor solid electrolyte material16. Memory cell 10 includes an electrochemically inert electrode 12, anelectrochemically active electrode 14, an ion conductor solidelectrolyte material 16, and an electrically insulating oxide layer 15separates the ion conductor solid electrolyte material 16 from theelectrochemically active electrode 14.

The ion conductor solid electrolyte material 16 is between theelectrochemically inert electrode 12 and the electrochemically activeelectrode 14.

The electrochemically active electrode 14 can be formed of any usefulelectrochemically active material such as, silver (Ag) or copper (Cu).The active electrode 14 can have any useful thickness, for example, from50 Angstroms to 5000 Angstroms. A top electrode (not shown) can bedisposed on the electrochemically active electrode 14. The top electrodecan be formed of any useful electrochemically inert metallic material,as described below.

The inert electrode 12 can be formed of any useful electrochemicallyinert metallic material. In many embodiments, the inert electrode 12 isformed of electrochemically inert metal such as, tungsten (W), nickel(Ni), molybdenum (Mo), platinum (Pt), gold (Au), palladium (Pd), andrhodium (Rh) for example. In some embodiments the inert electrode 12 hastwo or more metal layers, where the metal layer closest to the ionconductor solid electrolyte material 16 is electrochemically inert whileadditional layers can be electrochemically active. The inert electrode12 can also be referred to as a bottom electrode. The inert electrode 12can be, but need not be formed on a substrate. The substrate, ifutilized, can include silicon, a mixture of silicon and germanium, andother similar materials. FIG. 1A and FIG. 1B does not depict an optionalsubstrate.

The ion conductor solid electrolyte material 16 can be formed of anyuseful material that provides for the formation of conducting filaments18 within the ion conductor solid electrolyte material and extendbetween the electrochemically active electrode 14 and the inert metalcontact 12 upon application of an electric field EF+. In manyembodiments the ion conductor solid electrolyte material 16 is achalcogenide-type material such as, for example, GeS₂, GeSe₂, CuS₂,CuTe, and the like. In other embodiments the ion conductor solidelectrolyte material 16 is an oxide-type material such as, for example,WO₃, SiO₂, Gd₂O₃and the like.

Application of an electric field EF+ across the electrochemically activeelectrode 14 and the inert metal contact 12 allow metal cations (i.e.,silver ions) to migrate toward the inert metal contact 12, electricallyconnecting the inert metal contact 12 to the electrochemically activeelectrode 14. This electrical connection gives rise to the lowresistance state of the programmable metallization memory cell 10.

Reading the PMC 10 simply requires a small voltage applied across thecell. If the conducting filaments 18 electrically connect the inertmetal contact 12 to the electrochemically active electrode 14, theresistance will be low, leading to higher current, which can be read asa “1”. If conducting filaments 18 do not electrically connect the inertmetal contact 12 to the electrochemically active electrode 18, theresistance is higher, leading to low current, which can be read as a “0”as illustrated in FIG. 1B.

FIG. 1B is schematic diagram of an illustrative programmablemetallization memory cell 10 in a high resistance state. Application ofan electric field of opposite polarity FE− ionizes the conductingfilaments 18 and dissolves ions from the electrically conductingfilaments 18 back to the electrochemically active electrode 14, breakingthe electrical connection between the inert metal contact 12 to theelectrochemically active electrode 14 and gives rise to the highresistance state of the programmable metallization memory cell 10. Thelow resistance state and the high resistance state are switchable withan applied electric field and are used to store the memory bit “1” and“0”.

FIG. 2 is a schematic diagram of an illustrative programmablemetallization memory unit 20 including a semiconductor transistor 22.Memory unit 20 includes a programmable metallization memory cell 10, asdescribed herein, electrically coupled to semiconductor transistor 22via an electrically conducting element 24. Transistor 22 includes asemiconductor substrate 21 having doped regions (e.g., illustrated asn-doped regions) and a channel region (e.g., illustrated as a p-dopedchannel region) between the doped regions. Transistor 22 includes a gate26 that is electrically coupled to a word line WL to allow selection andcurrent to flow from a bit line BL to memory cell 10. An array ofprogrammable metallization memory units 20 can be formed on asemiconductor substrate utilizing semiconductor fabrication techniques.

FIG. 3 is a schematic diagram of an illustrative programmablemetallization memory array 30. Memory array 30 includes a plurality ofword lines WL and a plurality of bit lines BL forming a cross-pointarray. At each cross-point a programmable metallization memory cell 10,as described herein, is electrically coupled to word line WL and bitline BL. A select device (not shown) can be at each cross-point or ateach word line WL and bit line BL.

FIG. 4 is a flow diagram of an illustrative method of forming aprogrammable metallization memory cell with an oxide layer. FIGS. 5A-5Care schematic cross-section views of a programmable metallization memorycell with an oxide layer at various stages of manufacture.

At FIG. 5A an ion conductor solid electrolyte layer 16 is deposited onan inert electrode 12 at block 110 of FIG. 4. Both the ion conductorsolid electrolyte layer 16 and the inert electrode 12 can be formedusing known deposition methods such as physical vapor deposition,chemical vapor deposition, electrochemical deposition, molecular beamepitaxy and atomic layer deposition. While not illustrated, the inertelectrode 12 can be deposited on a substrate. The substrate includes,but is not limited to silicon, a mixture of silicon and germanium, andother similar material.

At FIG. 5B an oxide layer 15 or oxide forming layer 15 is deposited onthe ion conductor solid electrolyte layer 16 at block 120 of FIG. 4. Theoxide layer 15 or oxide forming layer 15 can be formed using knowndeposition methods, as described above. The oxide layer 15 or oxideforming layer 15 has a thickness in a range from 0.5 to 10 nanometers orfrom 1 to 5 nanometers. The oxide layer 15 can be formed of any usefulelectrically insulating oxide material such as, silicon (Si) oxide,aluminum (Al) oxide, titanium (Ti) oxide, halfnium (Hf) oxide,gadolinium (Gd) oxide or other transition metal oxide. The oxide forminglayer 15 can be formed of any material that have a very negativestandard reduction potential so that the material can form an oxidematerial when oxygen ions are present, such as, silicon (Si), aluminum(Al), and halfnium (Hf). Thus, the oxide forming layer 15 can combinewith oxygen ions to form an oxide layer 15.

At FIG. 5C an electrochemically active electrode 14 is deposited on theoxide layer 15 or oxide forming layer 15 at block 130 of FIG. 4. Theelectrochemically active electrode 14 can be formed using knowndeposition methods, as described above. Additional metal contactlayer(s) can be formed on the electrochemically active electrode 14. Inmany embodiments, at least one inert metal contact layer is deposited onthe electrochemically active electrode 14 (not shown).

FIG. 6 is a flow diagram of another illustrative method of forming aprogrammable metallization memory cell with an oxide layer. FIGS. 7A-7Dare schematic cross-section views of another programmable metallizationmemory cell with oxide layer at various stages of manufacture.

At FIG. 7A an ion conductor solid electrolyte layer 16 is deposited onan inert electrode 12 at block 210 of FIG. 6. The ion conductor solidelectrolyte layer 16 has a surface 16A or an exposed surface 16A. Boththe ion conductor solid electrolyte layer 16 and the inert electrode 12can be formed using known deposition methods such as physical vapordeposition, chemical vapor deposition, electrochemical deposition,molecular beam epitaxy and atomic layer deposition. While notillustrated, the inert electrode 12 can be deposited on a substrate. Thesubstrate includes, but is not limited to silicon, a mixture of siliconand germanium, and other similar material.

At FIG. 7B the surface 16A of the ion conductor solid electrolyte layer16 is oxidized to form an oxidized surface 16B at block 220 of FIG. 6.The surface 16A of the ion conductor solid electrolyte layer 16 can beoxidized utilizing any useful oxidation technique such as thermaloxidation, plasma oxidation, or UV oxidation, for example. In manyembodiments the ion conductor solid electrolyte material 16 is achalcogenide-type material such as a germanium rich solid (e.g., GeS₂)electrolyte, for example. In this example, the oxidized surface 16B willinclude germanium oxide.

FIG. 7C illustrates an oxide layer 15 or oxide forming layer 15deposited on the ion conductor solid electrolyte layer 16 at block 230of FIG. 6. The oxide layer 15 or oxide forming layer 15 can be formedusing known deposition methods, as described above. The oxide layer 15or oxide forming layer 15 has a thickness in a range from 0.1 to 10nanometers or from 1 to 5 nanometers. The oxide layer 15 can be formedof any useful electrically insulating oxide material such as, silicon(Si) oxide, aluminum (Al) oxide, titanium (Ti) oxide, halfnium (Hf)oxide, gadolinium (Gd) oxide or other transition metal oxide. The oxideforming layer 15 can be formed of any material that have a very negativestandard reduction potential so that the material can form an oxidematerial when oxygen ions are present, such as, silicon (Si), aluminum(Al), and halfnium (Hf). Thus, the oxide forming layer 15 can combinewith oxygen ions to form an oxide layer 15. In many embodiments theoxide forming layer 15 combines with oxygen ions from the oxidizedsurface 16B of the ion conductor solid electrolyte layer 16 (e.g., thegermanium oxide described above).

FIG. 7D illustrates an electrochemically active electrode 14 depositedon the oxide layer 15 or oxide forming layer 15 at block 240 of FIG. 6.The electrochemically active electrode 14 can be formed using knowndeposition methods, as described above. Additional metal contactlayer(s) can be formed on the electrochemically active electrode 14. Inmany embodiments, at least one inert metal contact layer is deposited onthe electrochemically active electrode 14 (not shown).

The oxide layer 15 described herein serves as an ionic barrier layerthat hinders or prevents ionic transport between the solid electrolyte16 and the electrochemically active electrode 14 of the programmablemetallization memory cell when an electrical bias is not present on theprogrammable metallization memory cell. For example, in the absence ofan electrical bias across the programmable metallization memory cell,oxygen ions migrate from the solid electrolyte 16 to the oxide layer 15increasing the ionic barrier properties of the oxide layer 15 andtherefore increasing the data state retention property of theprogrammable metallization memory cell.

The oxide layer 15 can be converted to a more ionic conductive phasewhen a negative electrical bias is applied to the programmablemetallization memory cell. Thus during a reset operation on theprogrammable metallization memory cell oxygen ions can migrate from theoxide layer 15 to the solid electrolyte 16 decreasing the ionic barrierproperties of the oxide layer 15. Overall, the oxide layer 15 serves asa variable barrier to ionic transport between the solid electrolyte andthe electrochemically active electrode of the programmable metallizationmemory cell (depending on an applied electrical bias), which enhancescell data state retention.

Thus, embodiments of the PROGRAMMABLE RESISTIVE MEMORY CELL WITH OXIDELAYER are disclosed. The implementations described above and otherimplementations are within the scope of the following claims. Oneskilled in the art will appreciate that the present disclosure can bepracticed with embodiments other than those disclosed. The disclosedembodiments are presented for purposes of illustration and notlimitation, and the present invention is limited only by the claims thatfollow.

1. A programmable metallization memory cell comprising: anelectrochemically active electrode and an inert electrode; an ionconductor solid electrolyte material between the electrochemicallyactive electrode and the inert electrode; an electrically insulatingoxide layer separating the ion conductor solid electrolyte material fromthe electrochemically active electrode; and a layer of germanium oxideseparating the electrically insulating oxide layer and the ion conductorsolid electrolyte material.
 2. The programmable metallization memorycell of claim 1 wherein the electrically insulating oxide layer has athickness in a range from 1 to 5 nanometers.
 3. The programmablemetallization memory cell of claim 1 wherein the electrically insulatingoxide layer comprises a metal oxide.
 4. The programmable metallizationmemory memory cell of claim 1 wherein the electrically insulating oxidelayer comprises Si.
 5. The programmable metallization memory memory cellof claim 1 wherein the ion conductor solid electrolyte materialcomprises a chalcogenide material.
 6. The programmable metallizationmemory cell of claim 5, wherein the electrically insulating oxide layercomprises Si, Al, or Hf.
 7. A programmable metallization memory cellcomprising: an electrochemically active electrode and an inertelectrode; an ion conductor solid electrolyte material between theelectrochemically active electrode and the inert electrode, the ionconductor solid electrolyte material having an oxidized surface,comprising germanium oxide; an oxide forming layer separating theoxidized surface of the ion conductor solid electrolyte material fromthe electrochemically active electrode.
 8. The programmablemetallization memory cell of claim 7 wherein the oxide forming layer hasa thickness in a range from 1 to 5 nanometers.
 9. The programmablemetallization memory cell of claim 7 wherein the ion conductor solidelectrolyte material comprises a chalcogenide material.
 10. Theprogrammable metallization memory cell of claim 7 wherein the oxideforming layer comprises Si, Al, or Hf.
 11. A programmable metallizationmemory cell comprising: an electrochemically active electrode and aninert electrode; an ion conductor solid electrolyte material between theelectrochemically active electrode and the inert electrode, the ionconductor solid electrolyte material provides for formation ofconducting filaments within the ion conductor solid electrolyte materialthat extend between the electrochemically active electrode and an inertelectrode upon application of an electric field; and an electricallyinsulating oxide layer separating the ion conductor solid electrolytematerial from the electrochemically active electrode.
 12. Theprogrammable metallization memory cell of claim 11 wherein theelectrically insulating oxide layer has a thickness in a range from 1 to5 nanometers.
 13. The programmable metallization memory cell of claim 11wherein the electrically insulating oxide layer comprises a metal oxide.14. The programmable metallization memory memory cell of claim 11wherein the electrically insulating oxide layer comprises Si.
 15. Theprogrammable metallization memory memory cell of claim 11 wherein theion conductor solid electrolyte material comprises a chalcogenidematerial.
 16. The programmable metallization memory cell of claim 11further comprising a layer of germanium oxide separating theelectrically insulating oxide layer and the ion conductor solidelectrolyte material.
 17. The programmable metallization memory cell ofclaim 16 wherein the electrically insulating oxide layer comprises Si,Al, or Hf.